Many handheld tools, such as chain saws, employ the two-mass principle, wherein the handle or handles and the fuel tank are separated from the engine. Springs suspending the engine base on a handle member greatly reduce vibrations in the handle or handles providing better working conditions for a user.
The engine base includes the engine with its movable parts, a centrifugal clutch to the chain, a chain brake and a kickback guard. The handle member includes a front and a rear handle, as well as a fuel tank.
The rear handle is in general formed integrally with the fuel tank in the handle member, preferably from a plastics material. The handle member can be manufactured by injection molding in two separate parts, which are not necessarily identical, but which are intended to be joined together along a circumferential line. The method of joining the two parts of the handle member is in general vibration welding, which includes a series of vibrations with a high frequency and a low amplitude, resulting in a joint along the circumferential line.
Since vibration welding of two pieces requires a sufficient thickness of the material to be welded, the walls of the handle member in several places have a greater thickness in the area of the joint. This will in turn mean that the weld will in several places be located at a protuberance, extending a distance from the surrounding surfaces. Especially on the underside of the handle member, this means that there is a protruding ridge, the weld, along the underside of the handle member, i.e. on the underside of the tool. When placing the tool on the ground this often means that the tool does not stand in a steady position but tends to lean over towards one side or the other. When cutting branches with a chain saw, the underside of the handle unit will sometimes be pushed over logs and branches. This tends to dirty and scratch the underside of the tool thereby impairing its appearance. These problems may be alleviated with embodiments of the disclosed handle member.